1. Field of the Invention
The present invention relates to a solid-state laser device, and in particular, to a solid-state laser device in which an excitation light source and a solid-state laser medium are accommodated inside a laser chamber.
The present invention also relates to a photoacoustic measurement device using such a solid-state laser device.
2. Description of the Related Art
Hitherto, as one image inspection method which can noninvasively inspect a state inside an object, such as a living body, an ultrasonography method has been known. In ultrasonography, an ultrasound probe which can transmit and receive an ultrasonic wave is used. For example, if an ultrasonic wave is transmitted from the ultrasound probe to the living body, the ultrasonic wave advances through the inside of the living body, and is reflected from a tissue interface. The reflected ultrasonic wave is received by the ultrasound probe, and a distance is calculated based on the time until the reflected ultrasonic wave returns to the ultrasound probe, whereby it is possible to image a status inside the living body.
Furthermore, photoacoustic imaging which images the inside of a living body using a photoacoustic effect is known. In photoacoustic imaging, in general, the inside of the living body is irradiated with pulsed light, such as a pulsed laser beam. Inside the living body, a living body tissue absorbs energy of pulsed light, and an ultrasonic wave (photoacoustic signal) is generated due to adiabatic expansion caused by energy. The photoacoustic signal is detected by an ultrasound probe or the like, and a photoacoustic image is constituted based on a detection signal, whereby it is possible to visualize the inside of the living body based on the photoacoustic signal.
In a measurement of a photoacoustic wave, in general, it is necessary to emit pulsed light with high intensity, and for example, a flash lamp excited solid-state laser device is widely used for a light source. This type of solid-state laser device has, for example, a solid-state laser medium which is formed in a rod shape, and a flash lamp which excites the solid-state laser medium. In many cases, the solid-state laser medium and the flash lamp are accommodated inside a laser chamber having an internal space. In general, the inner wall surface of the laser chamber is provided with a reflection surface or a diffusion surface to allow efficient irradiation of the solid-state laser medium with excitation light emitted from the flash lamp, and a refrigerant which cools the solid-state laser medium and the flash lamp is supplied into the internal space of the laser chamber.
The excitation light source, such as the flash lamp, is a consumable, and needs to be replaced regularly. Furthermore, there is a widespread demand for reduction in the size of the solid-state laser device, in addition to a case of being used for measuring the photoacoustic wave.
JP1998-125993A (JP-H10-125993A) and JP1998-125991A (JP-H10-125991A) disclose an example of a solid-state laser device in which replacement of an excitation light source or reduction in size of the device is considered.
That is, JP1998-125993A (JP-H10-125993A) discloses a solid-state laser device in which an excitation lamp having a straight rod shape and a solid-state laser medium formed in a rod shape are accommodated inside a laser chamber in a state of being close to each other in parallel to each other. JP1998-125993A (JP-H10-125993A) discloses that an optical path between one (rear mirror) of a pair of resonator mirrors and the solid-state laser medium is bent in a transverse direction by the mirror in order to prevent enlargement of the solid-state laser device in the longitudinal direction of the solid-state laser medium. Furthermore, JP1998-125993A (JP-H10-125993A) discloses that, for replacing the rod-shaped excitation lamp, the excitation lamp is pulled out of the laser chamber in the lamp longitudinal direction, and the mirror is rotated along with a holder thereof in order to secure a space for pulling out.
JP1998-125991A (JP-H10-125991A) discloses a solid-state laser device in which an excitation lamp and a solid-state laser medium formed in a rod shape are accommodated inside a laser chamber. JP1998-125991A (JP-H10-125991A) also discloses that an optical path between one (rear mirror) of a pair of resonator mirrors and the solid-state laser medium is bent in a transverse direction by the mirror in order to prevent enlargement of the solid-state laser device in the longitudinal direction of the solid-state laser medium.